Continuous process batch-operated reverse osmosis system with in-tank membranes and circulation

ABSTRACT

A reverse osmosis system and method for operating the same includes a pressure tank having a first end and a second end, the pressure tank has a first volume adjacent to the first end and a second volume adjacent to the second end and a third volume between the first volume and the second volume and a fluid passage fluidically coupling the second volume to the first volume. The reverse osmosis system also includes a plurality of membranes disposed within the third volume generating permeate and a permeate manifold receiving permeate from the membranes and fluidically communicating permeate out of the pressure tank. A feed line couples feed fluid into the pressure tank. A first pump pressurizes the feed line. A second pump is disposed within the tank and circulates brine fluid from the second volume through the fluid passage.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/159,532 filed on Mar. 12, 2009. The disclosure of the aboveapplication is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to reverse osmosis systems,and, more specifically, to a batch operated reverse osmosis system thatmay be operated as a continuous process.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

Reverse osmosis systems are used to provide fresh water from brackish orsea water. A membrane is used that restricts the flow of dissolvedsolids therethrough.

A reverse osmosis system involves pressurizing a solution with anapplied pressure greater than an osmotic pressure created by thedissolved salts within the solution. The osmotic pressure is generallyproportional to the concentration level of the salt. The approximateosmotic pressure in pounds-per-square-inch is the ratio of the salt massto water mass times 14,000. A one-percent solution of salt would have anosmotic pressure of about 140 psi. Ocean water typically has a 3.5percent concentration and an osmotic pressure of 490 psi.

Water extracted from a reverse osmosis system is called permeate. As agiven batch of saline solution is processed by the reverse osmosismembrane, the concentration of the solution is increased. At some point,it is no longer practical to recover permeate from the solution. Therejected material is called brine or the reject. Typically, about 50% ofrecovery of permeate from the original volume of sea water solutionreaches the practical limit in standard seawater RO systems.

Reverse osmosis systems typically have several components that are undervery high pressures that may exceed 1,000 psi. These components includemembrane housings, brine tanks, pumps and interconnecting pipes.Providing reinforced components increases the cost of the reverseosmosis system.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

The present disclosure provides a system that reduces the number ofcomponents that must be reinforced to withstand pressures compared toprior known systems.

In one aspect of the invention, a reverse osmosis system includes apressure tank having a first end and a second end, the pressure tank hasa first volume adjacent to the first end and a second volume adjacent tothe second end and a third volume between the first volume and thesecond volume and a fluid passage fluidically coupling the second volumeto the first volume. The reverse osmosis system also includes aplurality of membranes disposed within the third volume generatingpermeate and a permeate manifold receiving permeate from the membranesand fluidically communicating permeate out of the pressure tank. A feedline couples feed fluid into the pressure tank. A first pump pressurizesthe feed line. A second pump is disposed within the pressure tank andcirculates brine fluid from the second volume through the fluid passage.

In another aspect of the invention, a method of performing reverseosmosis in a system that includes a pressure tank having a first end anda second end, the pressure tank has a first volume adjacent to the firstend, a second volume adjacent to the second end and a third volumebetween the first volume and second volume and a fluid passagefluidically coupling the second volume to the first volume includescommunicating feed fluid to the pressure tank, increasing the pressurewithin pressure tank with a pump disposed within the inner chamber,generating permeate at a plurality of membranes disposed within thethird volume, fluidically communicating the permeate out of the pressuretank and circulating brine from the membranes from the second volume tothe first volume using a circulation pump.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1 is a cross-sectional view of a first embodiment of a reverseosmosis system according to the present disclosure.

FIG. 2 is a radial cross-sectional view of the tube sheet of FIG. 1.

FIG. 3 is a cross-sectional view of a second embodiment of the presentdisclosure.

FIG. 4 is a schematic view of a turbocharger for use in an alternativeconfiguration of FIG. 1.

FIG. 5 is a cross-sectional view of an eductor according to the presentdisclosure.

FIG. 6 is an electromagnetic pump that may be used in place of therecirculation pump of FIG. 1.

FIG. 7 is a cross-sectional view of a third embodiment of the reverseosmosis system.

FIG. 8 is a cross-sectional view of a fourth embodiment of the presentdisclosure.

FIG. 9 is a cross-sectional view of a fifth embodiment of the reverseosmosis system according to the present disclosure.

FIG. 10 is a cross-sectional view of a sixth embodiment of the reverseosmosis system according to the present disclosure.

FIG. 11 is a cross-sectional view of a seventh embodiment of the reverseosmosis system according to the present disclosure.

FIG. 12 is a cross-sectional view of an eighth embodiment of the reverseosmosis system according to the present disclosure.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses. Forpurposes of clarity, the same reference numbers will be used in thedrawings to identify similar elements. As used herein, the phrase atleast one of A, B, and C should be construed to mean a logical (A or Bor C), using a non-exclusive logical or. It should be understood thatsteps within a method may be executed in different order withoutaltering the principles of the present disclosure.

Referring now to FIG. 1, a first embodiment of a reverse osmosis system10 is illustrated. The reverse osmosis system 10 includes a pressuretank 12 that includes a housing 14 and a cover 16. The housing 14 may bea cylindrical housing having a longitudinal axis 18. A cover 16 issecurely fastened to the housing 14 during the reverse osmosis processto maintain a pressurized condition therein. The cover 16 may be openedfor servicing components within the pressure tank 12. The pressure tank12 may have a longitudinal axis 18 should the system be cylindrical.

The pressure tank 12 may be divided into three different volumes thatinclude a first volume 26 (adjacent to a first end of the pressure tank12, as illustrated in FIG. 1), a second volume 28 (adjacent to thesecond end of the pressure tank 12) and a third volume 30 (between thefirst volume 26 and the second volume 28). The first volume 26 isseparated from the second volume 28 by the third volume 30.

A fluid passage 34 may communicate fluid between the second volume 28and the first volume 26. The fluid communication process will be furtherdescribed below. The fluid passage 34 may be formed by a pipe betweenthe first volume 26 and the second volume 28.

A plurality of membranes 40 are disposed in the third volume 30. Themembranes 40 may be arranged away from a first end 42 of the thirdvolume near a second end 44 of the inner chamber 30. The membranes 40may be disposed within a membrane housing or tube 46. The membranes 40allow permeate to pass therethrough. Permeate is collected in acollection pipe 48 which is disposed in each of the membrane housings46. Only one collection pipe 48 for one membrane 40 is illustrated forsimplicity. Each membrane has a collection pipe 48. Each permeatecollection pipe 48 is in fluid communication with a permeate manifold50. The permeate manifold 50 fluidically communicates the permeate outof the pressure tank 12 using a permeate outlet pipe 52.

The membrane housings 46 may be secured by one or more tube sheets. Inthis example, a first tube sheet 54 and a second tube sheet 56 are used.The tube sheets 54, 56 may be formed from various lightweight materialsince differential pressures acting on the tube sheets are low. The tubesheets 54, 56 may, for example, be formed from a sheet metal, plastic orother lightweight material. The tube sheet 56 may be sealed to oragainst the wall of housing 14. The tube sheet 54 may not extend acrossto housing 14. At least one tube sheet 54, 56 separates and prevents theflow of brine directly between the second volume 28 and third volume 30.The sheets 54, 56 ensure the brine passes through tubes 46. In thisembodiment, the tube sheets 54, 56 orient the housings 46 in a directionparallel with the longitudinal axis 18 of the pressure tank 12. A numberof housings 46 and thus a number of membranes 40 may be disposed withinthe pressure tank 12. As will be illustrated below, sixteen housings 46and thus sixteen membranes 40 are disposed. Various numbers of membranes40 may be used.

A circulation pump 62 is used to circulate fluid from the second volume28 to the first volume 26. The movement of fluid from the second volume28 circulates through the fluid passage 34 to the first volume 26 andultimately into the third volume 30. The direction of circulation isillustrated by arrows 64.

The circulation pump 62 may be driven by a motor 66. The motor 66 may bea submersible motor 66. The motor 66 may be located at various locationswithin the second volume 28 or within the third volume 30 includingdirectly adjacent to the pump or included as part of the circulationpump 62. The motor 66 may be coupled to the pump 62 by a shaft 68extending therebetween. The circulation pump 62 may be located in otherplaces within the pressure tank 12 including within the first volume 26.

A low-pressure supply pipe 70 may be used for supplying low-pressurefeed fluid into the pressure tank 12. More specifically, the feed pump72 may communicate low-pressure feed fluid through the housing 14. Thefeed pump 72 may be in fluid communication with the supply pipe 70. Thefeed pump 72 may increase the pressure of the low-pressure fluid. Thefeed pump 72 may be coupled to a feed motor 74. The feed motor 74 may bea submersible motor used for driving the feed pump 72. The feed pump 72may have an output in fluid communication with a feed manifold 76. Thefeed manifold 76 may have a plurality of feed manifold outlets 78. Thefeed manifold outlets 78 may be disposed adjacent to or near an end ofthe membrane housings 46 nearest the first end 42. Thus, fresh feedfluid is thus provided near the membranes and reduce mixing with theincreased salinity fluid within the pressure tank is achieved.

The pump 72, the motor 74, the feed manifold 76 and the feed manifoldoutlet 78 may all be disposed within the third volume 30.

A distribution plate 80 may be disposed across pressure tank 12. Thedistribution plate 80 may be mechanically coupled to the inner wall 14of the pressure tank 12. Various fastening means may be used. Removablefasteners allow access to the membranes after the cover is removed. Thedistribution plate 80 may have vanes 82 used for evenly distributing thefluid that is recirculated through the fluid passage 34 and minimizingthe turbulence and mixing of the elements within the third volume 30.

In operation, low-pressure feed fluid is provided through the feed pipe70. The pump 72 increases the pressure of the feed and also increasesthe pressure within the pressure tank 12. The feed fluid is communicatedadjacent to the membranes 40. After pressure has risen above the osmoticpressure, permeate from the permeate collection tube 48 is removed fromthe pressure tank 12 by the permeate manifold 50. The circulation pump62 circulates brine fluid in the second volume 28 through the fluidpassage 34 to the first volume 26. The recirculated brine fluid from thefirst volume then enters the third volume 30 through the distributionplate 80. Fluid then passes through membrane 40 to second volume 28.

Referring now to FIG. 2, a cross-sectional view of a tube sheet 56 takenin a direction perpendicular to the longitudinal axis 18 is set forth.As is illustrated, a plurality of membrane housings 46 are illustrated.In this embodiment, sixteen membrane housings are illustrated. However,various numbers of membrane housings including only one membrane housingmay be provided. The tube sheet 54 may also be configured in a similarmanner. The tube sheet 56 forces brine fluid to pass through the housing46 and the brine fluid not converted into permeate is routed into thesecond volume 28. The tube sheet 54 allows fluid to enter the membranehousing 46 from the third volume 30.

Referring now to FIG. 3, a second embodiment of a reverse osmosis system10′ is illustrated. In this embodiment, the motor 74 of FIG. 1 isreplaced with motor 174 and a shaft seal 176 in the housing 14 of thepressure tank. The motor 174 is located outside of the pressure tank 12and may provide a lower cost and high-efficiency motor than thesubmersible motor 74 illustrated in FIG. 1. A shaft seal 176 seals themotor shaft 178 from leakage from the pressure tank 12.

A non-submersible recirculation motor 150 may also be provided in placeof the recirculation motor 50. The recirculation motor 150 may also havea shaft 152 that is sealed in the exterior wall of the pressure tank 12by a shaft seal 154. The motor 150 is coupled to the recirculation pump62 that operates is described in the description of FIG. 1. Theremaining elements and the operation of the second embodiment of thereverse osmosis system 10′ is the same as described above with respectto FIG. 1.

Referring now to FIG. 4, the circulation pump 62 and the recirculationmotor 50 of FIG. 1 may be replaced by a turbocharger 210. Theturbocharger 210 may include a pump portion 212 and a turbine portion214. A common shaft 216 may be used to rotate the pump 212 in responseto the rotation of the turbine 214.

The turbine 214 may be in fluid communication with the pipe 76 andoutlet 78. The feed flow through the pipe 76 rotates the turbine whichin turn rotates the pump 212 to generate a recirculation current or flowwithin the pressure tank 12.

Referring now to FIG. 5, the outlets 78 may include an eductor 230. Theeductor 230 induces brine circulation. The brine flow from the feed pump72 is expelled at higher pressure due to the energizing effect of thehigh-feed flow velocity from the feed pump 72. The outlet 232 of theeductor 230 receives the feed fluid from the pump 72 which is mixed withbrine fluid 236 and thus the combined fluid 238 may not flow through amanifold 76 as described above.

Referring now to FIG. 6, an electromagnetic pump may replace the pump 62and motor 66 illustrated in FIG. 1. The electromagnetic pump 260 mayalso replace the motor 150 and pump 62 illustrated in FIG. 3. Powerlines 262 provide power to the electromagnetic pump to create electriccurrents and magnetic fields to provide a pumping action in the highlyconductive brine fluid. The electromagnetic pump 260 has no moving partsand thus has increased reliability.

Referring now to FIG. 7, another embodiment of the reverse osmosissystem 10″ similar to FIG. 1 is illustrated having a rechargingarrangement 310. The recharging arrangement 310 allows continuousoperation in a single-batch tank by purging of the brine with fresh feedonce a maximum concentration has been reached in the pressure tank 12.Brine is depressurized as it leaves the tank and incoming feed ispressurized before entering the tank. A turbocharger 312 may be used torecover some of the energy lost in the process. The turbocharger 312includes a pump portion 314 and a turbine portion 316. The turbineportion 316 provides brine fluid through brine pipe 318. The brine pipe318 may provide brine fluid to the turbine portion 316 through a valve320. The pump portion 314 may inject feed fluid under high pressurethrough a check valve 322. In addition to the increase in pressure fromthe pump portion 314, a charge pump 330 may be used to increase thepressure in the feed fluid. The feed fluid for the pump 330 may beprovided from a feed tank 350. The feed tank 350 may also provide feedfluid to the pump 72.

The charge pump 330 may be operated by a motor 362. The motor may becontrolled by a controller 364. The controller 364 may be a variablefrequency drive that is operated in response to a pressure sensor 366.The charge pump 330 operates during the recharge process. When the batchprocess has reached a final brine concentration, the pump 330 isenergized and the valve 320 is opened allowing the brine to be drawn infrom the first volume 26 through pipe 318. The brine from the firstvolume 26 is at a high pressure and thus the turbine portion 316 isrotated which in turn rotates the pump portion 314 to increase thepressure in the feed from the feed tank 350. The check valve 322 openswhen the pressure is sufficient to overcome the pressure tank pressureand allow the feed into the pressure tank within the second volume 28.When providing the feed into the inlet 370, flow within the pressuretank 14 is opposite to the arrows 64. The combination of the reversal offlow and the high rate of input from the fresh feed from the feed tankthrough the feed inlet 370 may reduce scale and foulants from themembrane which may be carried out through the pipe 318 during theprocess. The inlet may be at various locations including in the centerof the lower surface of the pressure tank. Feed fluid from the pipe 370may also travel up the membrane housings to reduce and remove thefoulants from the membrane 40. The speed of the pump 330 may becontrolled by the controller 364 which controls the speed of the motor362. Fluid from the pipe 318 that passes through the turbine 360 may beinput to a drain 374 at a reduced pressure.

The fluid that enters the drain 374 has a significantly lower pressurethan the fluid from the pipe 318 as reduced by the turbine portion 316.

Referring now to FIG. 8, another embodiment of the reverse osmosissystem 10′″ similar to that of FIG. 7 is illustrated having the motor 74and pump 72 removed and controlled by the charge pump 330 and motor 362.In this embodiment the charge pump 330 is provided directly after thefeed tank 350. After the charge pump 330, fluid may flow into the fluidmanifold or into the turbocharger 312. A valve 410 may be providedbetween the charge pump 330 and the turbocharger 312 to selectivelycontrol the input to the pump portion 322. During recharge the valve 410is opened to allow feed fluid to flow from the feed tank 350 through thecharge pump 330 and into the pressure tank 312 as described above. Inthis embodiment, the additional pump within the third volume 30 isremoved. Valves 410 and 320 are closed during batch operation and openedduring recharge operation.

Referring now to FIG. 9, another embodiment of the reverse osmosissystem 10″″ similar to FIG. 7 is illustrated. In this embodiment, a workexchanger 510 replaces the turbocharger 312. The work exchanger 510 isused to receive high-pressure fluid from the first volume 26 through thevalve 320 which is open during the recharge process and convert the workto useful energy (to pressurize the feed fluid into the pressure tank12). Feed fluid is provided into the pressure tank 12 using a boosterpump 572 that is coupled to a booster motor 514. The recharge processuses the flow work exchanger 510 to inject fresh feed into the pressuretank while removing an equal volume of concentrate through the pipe 318.The booster pump 572 is used to make up for pressure loss in the pipingand the work exchanger 510. During the recharge process, the valve 320is opened and the pump 512 is energized using motor 514. The pump 72 maycontinue to operate during the recharge process and thus the permeateproduction continues without interruption.

Referring now to FIG. 10, an embodiment of a reverse osmosis system10′″″ similar to FIG. 1 is illustrated. In this embodiment, anadditional tank 410 is fluidically coupled to the pressure tank 12. Thetank 410 may have an inlet pipe 412 that fluidically communicated fluidfrom the first volume of the pressure tank 12 into the fluid tank 410.Fluid is provided from the fluid tank 410 through an outlet pipe 412.The outlet pipe 412 may fluidically couple fluid into the third volumeof the pressure tank 12. A valve 414 may be used to control the flow outof the tank 410. The tank 410 increases the amount of feed that can beprocessed by a batch.

Referring now to FIG. 11, another embodiment similar to FIG. 1 isillustrated. In this embodiment, the pressure tank 12′ is increased inlength to increase the amount of fluid volume within the tank to insurea sufficiently long batch run. When the feed total dissolved solids(TDS) is high then additional tank volume may be needed to insure asufficiently long batch run. When the total dissolved solids are low,the smaller tank volume may be more appropriate. A tank extender 450with seals 452 may be used to increase the length of the tank 12′.Mechanical fasteners or the like may be used to mechanically couple theextender 450 to the housing 14 of the previous embodiments. The fluidpassage 34′ may also be extended so that fluid from the second volume 28may be communicated to the first volume 26.

Referring now to FIG. 12, another embodiment similar to FIG. 1 isprovided. In this example, easy access so that the membranes 40 may beeasily replaced is provided. In this embodiment, the membrane tubes 46extend through the second tube sheet 56. Brine fluid from the membranetubes 46 still enters the second volume 28.

A plurality of covers 510 is secured within the housing 14. The covers510 are adjacent to the membranes 40 so that the membranes may be easilyremoved from within the pressure tank 12. The covers 510 may be coupledto the bottom of the housing 14 by various methods, including, but notlimited to, bolting, snap rings, or other suitable methods. In thisembodiment, the permeate manifold 50′ is located outside of the pressuretank 12. The collection tubes 48′ extend through the covers 510. Toaccess the membrane elements, the covers 510 are removed. Prior toremoval of the covers 510, the collection tubes 48′ may be disassembledto allow disassembly of the covers 510.

A spacer 512 may be used to allow brine fluid exiting from the membraneto flow to the fluid passage 34. The spacer 512 may be a separatestructure or mechanically coupled to the covers 510.

It should be noted that the various components of the disclosure foreach of the figures may be interchanged. For example, either or bothmotors may be located outside the pressure tank or within the pressuretank 12. Likewise, the recharging systems illustrated in FIGS. 7-12 mayalso be interchanged with themselves or the other components. Thealternative components of FIGS. 4-6 may be individual in any embodimentseparately or in combination.

Those skilled in the art can now appreciate from the foregoingdescription that the broad teachings of the disclosure can beimplemented in a variety of forms. Therefore, while this disclosureincludes particular examples, the true scope of the disclosure shouldnot be so limited since other modifications will become apparent to theskilled practitioner upon a study of the drawings, the specification andthe following claims.

1. A reverse osmosis system comprising: a pressure tank having a firstend and a second end, the pressure tank has a first volume adjacent tothe first end and a second volume adjacent to the second end and a thirdvolume between the first volume and the second volume; a fluid passagefluidically coupling the second volume to the first volume; a pluralityof membranes disposed within the third volume generating permeate; apermeate manifold receiving permeate from the membranes and fluidicallycommunicating permeate out of the pressure tank; a feed line couplingfeed fluid into the pressure tank; a first pump pressurizing the feedline; a second pump disposed within the pressure tank circulating brinefluid from the second volume through the fluid passage.
 2. A reverseosmosis system as recited in claim 1 wherein said fluid passage isdefined by a pipe extending from the third volume to the first volume.3. A reverse osmosis system as recited in claim 1 wherein the first pumpis disposed within the pressure tank.
 4. A reverse osmosis system asrecited in claim 1 wherein the first pump is disposed within the thirdvolume.
 5. A reverse osmosis system as recited in claim 1 wherein thefirst pump is disposed outside the pressure tank.
 6. A reverse osmosissystem as recited in claim 1 further comprising a fluid distributionplate adjacent the first end of the pressure tank and separating thefirst volume and third volume.
 7. A reverse osmosis system as recited inclaim 6 wherein the fluid distribution plate extends across the pressuretank.
 8. A reverse osmosis system as recited in claim 1 furthercomprising an input manifold fluidically coupled to the feed line.
 9. Areverse osmosis system as recited in claim 8 wherein the input manifoldhas a plurality of outlets disposed adjacent to a respective input endof a manifold.
 10. A reverse osmosis system as recited in claim 9wherein the plurality of outlets comprises an eductor.
 11. A reverseosmosis system as recited in claim 1 wherein the membranes are disposedadjacent to the second end.
 12. A reverse osmosis system as recited inclaim 1 wherein the membranes are disposed within membrane tubes, saidmembrane tubes comprising collector tubes coupled to the permeatemanifold.
 13. A reverse osmosis system as recited in claim 12 furthercomprising a tube support supporting the membrane tubes within the innerchamber.
 14. A reverse osmosis system as recited in claim 13 wherein thetube support comprises a first tube support at a first membrane and asecond tube support at a second membrane end, said second tube supportextending across said pressure tank.
 15. A reverse osmosis system asrecited in claim 14 wherein the membrane tubes extend through the secondtube support.
 16. A reverse osmosis system as recited in claim 15wherein said second tube support is disposed adjacent to a respectivecover that seals the pressure tank, said collector tubes extendingthrough the cover.
 17. A reverse osmosis system as recited in claim 1wherein the second pump is disposed within the fluid passage.
 18. Areverse osmosis system as recited in claim 1 wherein the second pump iscoupled to a motor and shaft.
 19. A reverse osmosis system as recited inclaim 18 wherein the motor is adjacent to or within the fluid passage.20. A reverse osmosis system as recited in claim 1 wherein the secondpump comprises an electromagnetic pump.
 21. A reverse osmosis system asrecited in claim 1 wherein the second pump is coupled to a turbine. 22.A reverse osmosis system as recited in claim 1 wherein the first pump iscoupled to a first motor.
 23. A reverse osmosis system as recited inclaim 22 wherein the first pump is coupled to a motor is disposed withinthe first volume.
 24. A reverse osmosis system as recited in claim 1further comprising a turbocharger comprising a pump portion and aturbine portion, said turbine portion fluidically coupled to the firstvolume and said pump portion fluidically coupled to the second volume ofthe pressure tank.
 25. A reverse osmosis system as recited in claim 24further comprising a third pump coupled to said pump portion.
 26. Areverse osmosis system as recited in claim 25 wherein the third pumpcoupled to said pump portion through a first valve and the turbineportion is coupled to said pressure tank with a second valve.
 27. Areverse osmosis system as recited in claim 26 wherein during recharge ofthe pressure tank, said first valve is in an open position and saidsecond valve is in an open position and wherein during batch operationof the pressure tank, said first valve is in a closed position and saidsecond valve is in a closed position.
 28. A reverse osmosis system asrecited in claim 24 wherein the pump portion is fluidically coupled tothe pressure tank through a check valve.
 29. A reverse osmosis system asrecited in claim 25 wherein the third pump is in fluid communicationwith a feed tank.
 30. A reverse osmosis system as recited in claim 1further comprising a flow work exchanger having an input portion and anoutput portion, said input portion fluidically coupled to the firstvolume and said output portion fluidically coupled to the second volumeof the tank opposite the first end.
 31. A reverse osmosis system asrecited in claim 30 wherein the output portion is coupled to a boosterpump.
 32. A reverse osmosis system as recited in claim 30 wherein theflow work exchanger comprises a second input and is coupled to a feedtank through the second input.
 33. A reverse osmosis system as recitedin claim 32 wherein the feed tank is in fluid communication with thefirst pump.
 34. A reverse osmosis system as recited in claim 1 furthercomprising a secondary tank having an input pipe fluidically coupled tothe first volume and an outlet pipe fluidically coupled to the thirdvolume.
 35. A reverse osmosis system as recited in claim 34 furthercomprising a valve coupled within the outlet pipe.
 36. A method ofperforming reverse osmosis in a system that includes a pressure tankhaving a first end and a second end, the pressure tank has a firstvolume adjacent to the first end, a second volume adjacent to the secondend and a third volume between the first volume and second volume and afluid passage fluidically coupling the second volume to the firstvolume, said method comprising: communicating feed fluid to the pressuretank; increasing the pressure within pressure tank with a pump;generating permeate at a plurality of membranes disposed within thethird volume; fluidically communicating the permeate out of the pressuretank; and circulating brine from the membranes from the second volume tothe first volume using a circulation pump.
 37. A method as recited inclaim 36 wherein the steps of communicating, increasing, generating,fluidically communicating and circulating are performed during batchoperation of the pressure tank.
 38. A method as recited in claim 37further comprising, during recharge operation of the pressure tank,performing the steps of: removing brine fluid from the pressure tank;and introducing recharging feed fluid into the pressure tank.
 39. Amethod as recited in claim 37 wherein removing brine fluid from the tankcomprises removing brine fluid from the first volume of the tank andwherein introducing recharging feed comprise introducing recharging feedinto a second volume of the pressure tank.
 40. A method as recited inclaim 37 wherein removing brine fluid from the tank comprises removingbrine fluid from the tank through a turbine portion of a turbochargerand wherein introducing recharging feed fluid into the pressure tankcomprises introducing feed fluid into the pressure tank through a chargepump coupled to the turbine, and further comprising increasing therecharging feed fluid pressure with the charge pump.
 41. A method asrecited in claim 36 wherein communicating feed into the pressure tankcomprises communicating feed fluid into the pressure tank through a feedsupply coupled to the charge pump.
 42. A method as recited in claim 36wherein communicating feed fluid comprises communicating feed fluid intothe pressure tank adjacent to the membranes.
 43. A method as recited inclaim 36 wherein communicating feed fluid comprises communicating feedfluid into the pressure tank adjacent to the membranes through aneductor.